Masculinization of chinook salmon ( Oncorhynchus tshawytscha) by immersion treatments using 17α-methyltestosterone around the time of hatching

Abstract

Groups of monosex female eyed eggs and newly hatched alevins received single immersions in 17α-methyltestosterone at 20 or 200 μg/l for 30, 60 or 120 min at 10°C. Three groups received a second immersion treatment 8 days later at 200 μg/l for 30, 60 or 120 min. The fish were sampled at 122 days post-hatch and the results indicated that all the treatments affected gonadal morphology. The most significant effect was at 200 μg/l where 82–100% males were produced as compared to 0% males in the monosex female control group. The percentage of males was increased by double immersion treatments. An increase in the treatment duration at 20 μg/l also increased the percentage of males. Survival was high in all groups and the mean weights of the treated groups were larger than the control group at 122 days post-hatch. This study demonstrates that the sex differentiation of chinook salmon is very labile and easily influenced by androgen treatment around the time of hatching. A simplified technique for producing phenotypic males consists of two 2-h immersions at 200 μg/l 17α-methyltestosterone in incubation water of 10°C, 1 week apart, commencing during final hatching.